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Could a 30 knot direct crosswind make a Learjet roll over 90 degrees?
Could a 30 knot direct crosswind really make a Learjet roll over 90 degrees?
A recent incident has prompted this question, but it's not explicitly about that incident (with its ongoing investigation).

Welcome to aviation.SE! That accident is still under investigation, and we have a consensus on this site of not speculating about accidents where there is no official report. However, this question might be useful.

@Pondlife, this question is not about the accident though, it is about the effect of a cross-wind.

Hi! you seem to have created two accounts (https://aviation.stackexchange.com/users/35603 and https://aviation.stackexchange.com/users/35605) You have registered neither. If you want you can register one and ask for them to be merged (https://aviation.stackexchange.com/help/merging-accounts).

While I agree with @JanHudec, I'm voting to close this question since it contradicts with the following: "No questions about accident speculation" and "hypothetical question" from the help center.
Rewording the question to make the crosswind the main point of the post would  IMHO be the best solution.

"could a 30 knot cross wind really make a Learjet roll over" seems pretty clear to me, sorry, I felt it necessary to add to what seemed to be an uncharacteristicly lacking response.  I usually agree with Jan too, but info is important for safety.

I've edited to remove the explicit reference to the incident, referring to it only as the prompt for the question.

You might want to check out XC-VMC. Give the aircraft registration to your favorite search engine for additional information.

The question still is very hypothetical - Do we want that?

@JanHudec That's right, but I thought it would be useful to mention it to a new user, and to encourage people to focus on the general principle rather on one specific accident.

It only ever makes sense to talk about cross-wind when the ground is involved. While the aircraft flies, it moves relative to the air and how fast the air is moving relative to ground only affects ground speed and track. If the air is moving smoothly, it can't turn anything over. Only thing that could bank an aircraft over is strong turbulence.
Natural turbulence of a 30 knot wind is unlikely to be strong enough to bank a Learjet 35 significantly, but a wake vortex close behind a heavy aircraft possibly could. The separation minima are there to prevent encountering wake turbulence on approach.

The original question was could the wind roll the Learjet 90 degrees and cause it to crash while landing in gusty winds.
PART 1  THE DANGERS OF WINDY CONDITIONS CAUSING AN AIRCRAFT TO STALL - LEADING TO A ROLL AND CRASH
Ground speed is affected by wind speed and direction,  which can make holding a ground track (landing pattern) in wind problematic.
Gusting wind presents a danger with tailwinds as a gust can lower airspeed and cause a stall.  For example, an aircraft that stalls at 50 knots Indicated Air Speed will approach at around 1.2 - 1.3 V stall, around 60-65 knots IAS.
A 15 knot tailwind gust will put IAS at or below stall in level flight.  An alert pilot will pitch down and add power to avoid stalling.
What compounds the problem is holding the ground track in the wind. A 20 knot tailwind will make 65 knots IAS 85 knots ground speed.  A pilot who tries to hold the track with a steeper banked turn risks an accelerated stall.  Stall speed for a 45 degree turn is 20% higher, now 60 knots.  A 15 knot tailwind gust while turning would disastrously lower IAS to 50 knots.
Note also that a lull in headwind similarly would create a loss of airspeed.
So close monitoring of airspeed is essential in these situations, as well as an awareness of wind speed, direction, and gusts.  While there are steady breezes,
calm air will never gust or change direction.
PART 2  EFFECT OF CROSSWIND ON AIRCRAFT IN FLIGHT
An aircraft in flight is unaffected by any CONSTANT wind as it moves with the wind. The only motion relative to the wind is velocity caused by thrust and control inputs.  Imagine the entire air mass and the plane moving through the sky.  One way of looking at it is the motion of the earth and moon.  The moon orbits the earth, but BOTH share the same motion around the sun.
There for a constant cross wind will not roll an aircraft. However, a GUST or change in wind from the side will put a side force on an aircraft as follows:

Gust strikes side of aircraft, pushing it sideways and rolling it away from wind.
Plane moves sideways at speed equal to gust, or gust begins to pass.  Nose will start to point into gust as a result of change in relative wind.
When gust has passed, plane now has side force on OTHER SIDE due to "push" from gust and slip from roll and rights itself.  Nose will point back to original course.

It is unlikely a 30 knot gust will roll a Learjet 90 degrees while it is in cruising flight, or even when it has reduced speed to land.
But, tragicly, the 90 degree roll is the death knell of a stalled aircraft near the ground.  This is what we work to avoid.
PART 3 WAKE TURBULENCE
Wake turbulence from a large aircraft would also be capable of rolling a Lear Jet if it followed too closely.  The vortex flows, especially when the aircraft is pitched up into a high induced drag configuration (even more so with slats and flaps fully deployed) is very dangerous to smaller aircraft.
PART 4 TURBULENCE CREATED BY TERRAIN OR LARGE BUILDINGS
This one is for mountain flyers, who must beware of rotors that form in the lee of the peaks, as well as strong updrafts on the windward side.  This will turn a smooth wind flow into an unpredictable pattern that can suddenly roll an aircraft.  Lenticular clouds over the mountains warn of the danger.


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When does fuel indicator indicate red index? C172
Full fuel is 56 gal and usable fuel is 53 for c172r. Other than when the fuel indicator is broken, when the fuel indicator indicate red index? Is there any fuel quantity setting to indicate red?

As always, the answer to this question is in the POH. You should always check the specific POH for the aircraft in question but you can usually find one for common aircraft (such as a 172) online. One such example is here.
Under the section on instruments, and specifically "fuel systems"

Fuel quantity is measured by two float-type fuel quantity transmitters
  (one in each tank) and indicated by two electrically-operated fuel quantity
  indicators on the left side of the instrument panel. An empty tank is
  indicated by a red line and the letter E. When an indicator shows an empty
  tank, approximately 1.5 gallons remain in a standard tank, and 2 gallons
  remain in a long range tank as unusuable fuel. The indicators cannot be
  relied upon for accurate readings during skids, slips, or unusual attitudes.

I'm pretty sure the "r" variant in your question is the 172 fitted with long range tanks.

This is different from a car then, right? When the fuel indicator touches the read area there, then you usually have still 10 % or so of usable fuel.

@PerlDuck ha yes, they are different to cars. There are 2 types of car drivers - those that fill up when the car is on quarter tanks, and those that wait until it is below the red line. You wont find a similar distinction of pilots, I assure you! I have literally never seen an aircraft even get close to the red lines on fuel gauges. SOP at my club is you need 9Gallons reserve on landing.

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Could the principle of owls' silent flight be used for stealth aircraft?
I was wondering about the ability of owls to fly so silently. Is it because they flap gently, they flap less often or do is their structure responsible? I was thinking their principle of stalking can be applied to stealth aircraft. Is it possible?

Not having jet engines helps.

Short answer-- "by being owls not airplanes"

Paper airplanes are pretty silent, but that's the "no engines" thing again. Gliders and parachutes are pretty silent too.

I disagree with putting this question off-topic.  Birds are the master aviators on this planet, so it would only make sense to include the OP in SE Aviation.

The question is about aviation: aircraft design is on-topic here. It may be a bit broad but it's eminently answerable. Voted to reopen.

Or can we put sensors on owls and send them on missions?....

Stealth has almost nothing to do with "silence", and is all about being invisible to radar.   When an owl learns to evade radar, let me know.

@Dave I heard somewhere that pigeons were used for military purpose (such as communication). Why not use other birds as well?

@ManuH They tried it with Mexican bats. Didn't go well.

Regardless of how little an owl flaps, it will flap more often than a stealth plane.

You know, in sci-fi-action movies, indeed "stealth!" helicopters usually means "silent" helicopters.

@Fattie Ah, good ol' "whisper mode"!

@mast ok I should have write "flying animal" (bats are not birds)

Only if those stealth aircraft were covered with feathers, flapped their wings, and flew at no more than 30 miles per hour.

Their primary wing feathers have an unusual structure incorporating a fringed, comblike leading-edge, which reduces wind noise.  The wing feathers also have an overall softness or flexibility.  The trailing-edge of the wing is also dominated by soft, fringed edges.  Even the underwing lining (covert) feathers have an unusual softness that plays a role in sound suppression.
See for example --
https://www.owlpages.com/owls/articles.php?a=7n ,
https://animals.howstuffworks.com/birds/owl-fly-silently1.htm .
Google "owl feather structure" for more.
I'll leave it mostly unsaid, as to whether any of these features are worth incorporating into a jet-powered aircraft.  Maybe some of these features might be applied to the intake or exhaust areas, in a more rigid metallic form?

I vote for fur covered wings on aircraft then :-)

+1 for the combination of this answer and your user name :-)

ha didn't even notice that, is a reference to flying gliders!

There are actually fans and such that are inspired by old feathers, e.g. https://cosmosmagazine.com/physics/turbine-blades-inspired-owls  and cooling fans for computers.  But I think part of the problem is that owl wings are low-speed aerodynamics, turbine blades are high-speed.  And even with GA planes, few if any actually have adequate mufflers, so the engine noise far outweighs noise from the wings &c.

Intake and exhaust areas of jet engines are already designed to be "acoustically soft" to reduce noise.

Modern jet engine exhausts already do make use of this - they have a shape that is reminiscent of a castle turret, but rounded off, precisely so that it merges the exhaust with the general wake in a blended manner.

OP didn't specify that they were thinking of jet-powered aircraft.  They could be considering quiet helicopters or prop-planes.

@EldritchWarlord It doesn't get any easier with piston-powered aircraft. Feathers on the wings are a bit less likely to reach auto-ignition temperatures with piston-powered aircraft, but they're about as unlikely to survive flight at 120 knots as they are flight at 500 knots. Fortunately for owls, they typically don't need to fly at 120 knots.

@DeltaLima haha - That reminds me of this answer.

The engineering to allow feathers to be grown on aircraft flight surfaces would be...fascinating. :-)

As soon as airflow starts to reach Mach 1 (the speed of sound) you'll get noise, so owls do it by flying very slow and suppressing big vortices, like some flying wings keeping flying for days without recharging.
The US tried silent aircraft during the Vietnam War Era, by combining slow-rotating propeller with extremely big and long exhaust systems. Worked quite well, so the aircraft was inaudible when flying at 200 ft. The aircraft were modified  Schweizer gliders, with increased inboard wing chord, and trike landing gear.
One was still in use by NASA a few years back.

In addition to quiet flyer's excellent answer:
Owls have large wings in relation to their body size and weight. One might think that no, their bodies are quite large, but actually owls are kind of fluffy flying feather balls: what you percieve as their bodies, is mostly air.
This leads to two things:

Low wing loading. Their large wings do not need to create as much lift per area unit as, say, with pigeons. This leads to less turbulence, which in turn means less sound. Because of low wing loading they also can fly with very little wing movement, also leading to less sound generation.
The fluffyness (for lack of a better word) suppresses turbulence in wing - body attachment area, and any other turbulence around owl body. This means, of course, less sound.

When combined with wing structure described in q f's answer, all these factors create a pretty much absolutely silent flight.
Check out this excellent BBC Earth clip comparing the sound different birds make when they fly, and why so.
As for the aplicability of these features in stealth aircraft, not likely, athough I strongly second PerlDuck's vote for fur covered wings on aircraft. The fact is, however, that there is no sense in making the wings or the airframe more silent, when the sound of the propulsion is orders of magnitude louder than any other part of the aircraft.
P.S. It's actually quite eery to encounter an owl in flight when it's dark. You can hear other birds when they fly in your vicinity, but owls, no, they just blast right by you totally silently, without a warning. They've scared me sh__less a couple of times out in the wild, and I'm pretty sure they enjoy it...

There's a tree-lined avenue near where I used to live where owls do swoops on people from behind, coming within inches of the top of your head and back up to the next tree. I'm never sure if they're doing it for fun or for practice or just to see what happens!

+1 for the BBC video link. It was the first thing that came to mind the moment I saw the question title.

Not just owls - you can't hear a hawk coming either.  Having a hawk fly over the audience's heads is a favourite stunt for raptor demos.

But you can hear a hawk fly past you. Owls, nope...

Search for  Owl X-ray pictures and you'll understand

@jpe61 Not if they don't flap. Which is kind of the point of the BBC clip - the noise birds make is from flapping, and owls avoid that by being ambush predators and only gliding.

@Graham this might be subspecies and/or speed dependend, as the one that flew by me in a birds of prey -show definitely made an audible "swishhh" :)

Fun fact: If an owl could turn its head by additional 90°, nobody would notice it can turn its head at all.

Stealth aircraft are built to reduce their observability in 3 main areas, with the goal of reducing the warning time an enemy has:

radar
optical and IR
sound

This is in order of detection range: Radar can find an aircraft potentially at hundreds of km, optical systems go to a few tens of km, and sound becomes a factor only when the aircraft is very near (at low altitude and high speed, you can get within 100 m of the target before you become audible).
The detection range also gives you the order of importance. Radar takes priority.
The sound produced by an aircraft is dominated by its engine noise. The air rushing over the skin makes some noise, but that's generally only audible when the engines are shut off. This means there's no benefit to reducing skin noise.
In addition:

a fringed, comblike leading-edge

This is a nightmare for radar stealth. You want the structure to be as simple and smooth as possible, because when you have a large number of surfaces in many directions, you get many radar returns. Improving audio stealth would compromise radar stealth.

“because every edge produces a strong radar return” – really? I think edges per se are pretty irrelevant to radar return, it's surface alignments that matter. Thus the very different approaches in the faceted F117 and smooth B2 or F-22/F-35 both make sense. Granted, the latter are probably a lot better not only in flight characteristics but also in stealth, but this has more to do with better materials and computer power than with absence of edges.

What you probably mean really are concave edges, in particular corner reflectors. But concavities can also help surpressing echo, c.f. RF anechoic chambers. The trick is to “trap” the signals between the opposing surfaces, and only let them escape greatly attenuated and scattered.

yeah, that was a brainfart.

This is the correct answer, since it actually addresses the applicability to aircraft that OP asked about instead of getting sidetracked with owl geometry.

a fringed, comblike leading-edge could in theory be made of a radar-transparent material, not metal, which could preserve radar stealth.  In supersonic aircraft leading edges get a lot of heating and aerodynamic forces, so this might only be viable for low-speed stealth drones (disguised as owls, like abligh suggests :)

https://en.wikipedia.org/wiki/Lockheed_YO-3 is an example of design when first two are not a concern (still not fluffy). Fun fact - in Museum of Flight (Seattle) it stands next to completely opposite approach - SR-71 - "so you can detect me - what are you going to do".

whereas with high altitude and/or low speed it's possible to hear a jet engine over 5 miles away, or a helicopter at 2 miles.

Owls' bodies are optimised for silent unpowered flight; even when owl flight is powered flight, it's powered by wing flapping (rather than jet engines or turboprops). At most I suspect you'll be able to help silence the noise from a body passing through the air; as gliders are rather quieter than light aircraft, I suspect this is the minority of the sound, at least until speeds get very fast where the aerodynamic and acoustic models will be very different anyway.
However, as "aircraft" is widely defined, perhaps they would be useful for a drone that for portions of its flight mostly glides silently at low-ish (owl-like) speeds, for covert photography, covert small payload delivery, or some other likely nefarious purpose. Heck, it could actually be disguised visually as an owl.

Maybe all those "owls" really are... Nah.

Expanding on the impact of audio levels on some mission profiles may be useful. [I remember reading about owl wings influencing prop blade design, but I'm drawing a blank on the specific project.] 'silent' glider designs also have some utility in an instance where you might want to pick up audio, and I've seen some draft ideas on the use of powered glider drones with loud speaker and microphone arrays for use in search and rescue applications.

If the other excellent answers roll off you like water off a duck's back, this may convince you:
What owls had to give up in exchange for quieter (not silent!) flight, is fast flying and flying on rainy days. Their feathers miss (most of) the oils that make other flying birds able to take quite a drenching without much trouble (and water birds even more so).
Planes crashing because of wet wings would be frowned upon, of course --- but the fixed wings would not have that problem; however any moisture would defeat this noise reduction. Only during landing & take-off noise reduction is really wanted (cruising altitude is too high to care); the added drag throughout the flight is (and added weight+drag when wet during takeoff+landing) will surely rule it out.
However, you can consider applications where it would be justified: If there's a large premium for silence, no need for high speed? Sounds like e.g. a specialized drone for observations to me. Then:  If it's raining, take out the regular spy-drone (as the rain covers the drone noise); if it's dry, your special 'owl-drone' goes out...  This more or less doubles your cost-of-ownership as you need two not one drone.

If your owl-drone could ride the thermals there wouldn't even be any need for engine sounds most of the time. Trouble is that during the day your owl-drone can be, er, seen (unless it can also be made see-through :) ). At night I presume there are fewer thermals generally to take advantage of (I'm not an aviation person).

@mikerodent based on your user name, I'd think you're not much of an owl person, either! ;)

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Why did my LGA-ORD flight make an S-shaped turn round the time it was passing a storm?
On a recent United UA1709 flight into Chicago (hit by a heavy storm at the time), I felt a noticeable descent, combined with two wide banks around 1 hour before landing. Looking at the flight path, I see an S shape that deviates from the original flight path.
Looking at the altitude readings here, the plane registered a descent of around 3000 fpm around the time of the turns from a cruising height of 30000 ft to 21000 ft. This descent took the plane under cloud cover and into the storm, so I am certainly confused as what motivated this flight path. Given that the flight was an hour away from landing, I find it hard to believe that this was a holding pattern of some sort.
Some more things that I noticed during this flight (not sure if relevant) was that a few minutes after this, I noticed lights indicating a plane flying directly above (hard to estimate distance given bad visibility). Furthermore, in-flight WiFi briefly cut out for a few minutes.
Can anyone explain what happened here?

The aircraft landed about 40 minutes after the first descent, not an hour later. The S-turn was during the 4-minute level-off at 21,000 and was about 30 minutes before landing. Most of the remaining 30 minutes appears to have just been flying the approach pattern around ORD.

It might help if you'd tell us where LGA and ORD actually are.

I find it hard to believe that this was a holding pattern of some sort.

Believe it. An hour before landing would be about the point at which the aircraft will start its descent to its destination. Almost certainly, air traffic control were delaying your flight for a few moments to ease insertion into the landing pattern at Chicago. Doing this at altitude burns less fuel than waiting until the aircraft is lower down.
The storms were incidental. Had the pilots been avoiding the weather they'd have diverted north or south and then resumed their route. A large S-bend wouldn't be necessary.

Based on your provided flight info, I looked up the track history on flightradar and did see some potential traffic conflict that might have tempted the controller to route your plane that way.
The first turn to the South appears to be a conflict with AAL 91, who was coming in from the North, also descending. AAL 91 executed a 90 right turn, while UAL 1709 turned left.

Now your flight is heading South. The controller had to turn you back at some point; if you keep going that direction you're going nowhere. That explains the second turn. The traffic above seems to be AAL 436, who was in an climb towards the West. It appears there were 3000 ~ 4000 ft of vertical separation when you pass each other.

The controller eventually sent your plane into the queue of planes landing at Chicago.
(For anyone interested, the area of interest is to the ENE of ORD, just near the shoreline. UTC time is 20191127 00:45)

Was this normal? Yes. Once a flight leaves cruise altitude, it is subject to "vectoring" (given headings to fly) by ATC. During ascent (from around 10,000 feet up to cruise altitude) and descent (from cruise altitude to Initial Approach Fix), it is common for ATC to route planes around to ensure they're safely separated. The exact traffic you encounter varies with traffic to/from other nearby airports, as well as weather (as you've noticed), so it is always a bit unpredictable.

That is a huge detour simply for collision avoidance.  While the first turn may have been to avoid a conflict, the circuitous path thereafter I would think to have been deliberate vectoring to delay the aircraft and slot them into the approach.

I agree with J that it looks more like a delay vector. But that doesn't explain the descent. Depending on where that small cell was to the north of them on the map. Not sure when that weather radar image was frozen. They could have been avoiding the cell and descending out of icing conditions.

@TomMcW Looking at the ADS-B data on flightaware, the first step descent down from cruise altitude was already mostly complete before the s-turn. The s-turn started at about 22,000 and the aircraft was level at 21,000 for most of the maneuver. It was given clearance for further descent about a minute after the s-turn was complete. The descent was just because it was time for the aircraft to begin its descent into ORD.

Storms have nothing to do with this. I'm a pilot who routinely flies into both Chicago O'Hare and La Guardia. The S-turns are because of flow control into busy airports. ATC normally tries to change speed of incoming aircraft but sometimes it's not enough and delay turns are required to ensure adequate separation. If they get really backed up due to bad weather or switching active runways, then holding may be required.

Since you mentioned storms I would imagine the pilots had requested a deviation from track/altitude to avoid bad weather. The storm you felt was problem the fringe of a bigger storm system and they would have been given/or requested a path/level where the storm activity was reduced. Wi-fi also suffers in storms.

the flight plan movements look very similar to the shape of the storm. So this could just be a visualization issue.


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Why does the stagnation point on airfoil move with the angle of attack?
What is the physical explanation for the reason the stagnation point is where it is? And, why does it move further down the lower side of the airfoil with an increase in angle of attack?

I imagine it is something to do with that being the balance of point of where it is easier for the air to go up and over or instead carry on down the lower side of the airfoil? but then if that's the case why does it move, possibly to do with the decrease in pressure on the top making it easier for more air to go up and over instead of along the bottom?

You are on the right track. As the pressure difference between above and below increases, the low pressure region above sucks more air, so the stagnation point moves down. I don't think it can be quantified without running the full fluid dynamics calculation though.

@JanHudec Yes it is the only reasonable explanation i have come to i just can't find any source anywhere to justify it.

At the stagnation point, the streamline is directly perpendicular to the airfoil. As angle of attack increases,  the streamline is no longer perpendicular to the leading edge (which is where the stagnation point is usually located at 0 angle of attack). This is the best explanation I can come up with for why the front stagnation point moves as it does.
The rear stagnation point is usually located at the trailing edge of the airfoil, thanks to the Kutta Condition which says that, "A body with a sharp trailing edge which is moving through a fluid will create about itself a circulation of sufficient strength to hold the rear stagnation point at the trailing edge." (according to wikipedia). The airflow around the airfoil, which is a body with a sharp trailing edge, keeps the rear stagnation point where it is.
This moving of the front stagnation point as the AoA increases is part of the reason why lift increases with increases in AoA.

If anyone can come up with a better explanation, please let me know. I feel this doesn't do justice to the question.

Pretty good explanation. If you consider the stagnation point where the air hits the wing (or vice versa), air above it goes over and air below it goes down.  If you change the angle of the wing, the air hits at a different point.

But once the angle of attack is increased it is not just the one streamline but multiple streamlines that are perpendicular to the flow which start to go over the airfoil. So what is determining how much of the airflow that decides to go back up and over instead of carrying on below the airfoil?

The streamline may, and does, curve before hitting the wing, so while it indeed is locally perpendicular at the stagnation point, it is not enough to determine it.

@IanHodges That is determined by the pressure difference. High pressure above and low pressure below means the airflow is far more likely to travel to the lower surface.

@ironduke97 i assume you mean low pressure above and high below? It seems the only logical explanation i just can't find any source that explains this movement

Yeah, that's my bad. I confused myself @IanHodges

Although a tad late; I'll have a go at this and I will use elementary yet powerful potential flow approach for this.
Suppose we start with the non-lifting case. Then, the forward stagnation point will be x/R = -1
.
Now let us rotate the cylinder clockwise. The mathematical representation is a vortex. Clearly, the stagnation point moves downward. One should view this point as the point where the induced velocity exactly opposes the velocity caused by the non rotating case. This also means that with increasing circulation, the stagnation point moves downward.
.
An airfoil can be thought of as a lifting cylinder to some abstraction. So, when the angle of attack is increased and a new steady state has been achieved (i.e. effect of shed vortex is diminished), the circulation must have increased. Hence the stagnation point moves to a lower position.
EDIT: To make it physical: A change in angle of attack leads to a change in vorticity and circulation. This is basically a consequence of fluid dynamics and boundary conditions. These in turn are a consequence of a new balance between pressure and shear forces!

stagnation point is the point with more pressure, always it's the first point that the flow faces an object. At that point, the flow has most Kinetic energy and it loses more of it in the first collide that makes pressure.at the other points, this flow doesn't have such as that energy so less energy makes less pressure.when the AoA change, the first point that the flow face will change. if we increase the AoA, the stagnation point goes down on the airfoil because the first point that flow faces comes down And conversely.

In fact the direction of flow near the front of the wing changes as the angle of attack changes.


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Are there any lift or lift coefficient equations which factor in the flap deflection angle?
I'm asking this because I tested a NACA 2412 wing with an adjustable flap in a subsonic wind tunnel and I'm getting the lowest Cl values for the highest  flap deflection angle.. which to my knowledge is theoretically wrong.
The inlet velocity is 15m/s. What is worrying me is that for a flap angle of 0 degrees, my cl value is a maximum. For 22.5 degrees, it gets less, and then for 45 degrees, it is the least. So the relationship is basically the inverse.
Note: the wing flap deflection is just to change the deflection angle of the flap; the wing area remains constant.
I'm guessing this could be due to increased turbulent flow after a certain flap deflection angle. That angle is what I am trying to determine.

Have you tried smaller defections such as 5, 10, 15? Maybe it's stalling prematurely due to excrescence/interference.

I'll try that and see how it goes, I guess I should get more realistic values

Are you measuring actual lift increase or are you comparing lift per angle of deflection? Because at low angles you get more lift per degree of flap but for higher flap angles you get more total lift, up to a point where the flow separates. Adding a slot helps delay that separation.

I think what you are seeing is that you can't get anywhere directly in flow dynamics.  Our intuition as pilots is that "adding flaps = more lift" and yet, it's actually much more complicated than that.  Adding flaps may move the CP (center of pressure) of the wing to a different arm from the CG, causing a change to angle of attack, causing X, which then causes Y, etc etc.  Extending the flaps changed some things that changed some other things and those second and third-order effects resulted in a higher C(L) and more lift.  Nothing can be examined in any kind of isolation.

Flaps shift the lift curve up and to the left causing a different very different cL at similar angles of attack. You cannot expect your results to make sense if you do not account for the shift in POSITION of the lift curve AS WELL AS the shift in SLOPE. I was surprised to realize that most airfoils STALL at a LOWER angle of attack when FLAPPED!


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Should IFR flight plans in the USA still have one waypoint per sector in 2023?
Alternate title: How come ATC has cleared aircraft direct from Laredo to Columbus 17 times?
If you hop on ForeFlight today (Feb 20 2023) and search for suggested routes between KLRD and KCMH you'll discover that the most cleared route (17x!) is KLRD GETTA.JAKTZ1 KCMH.  That's a thousand nautical miles and four ARTCCs between the departure point and the first fix.
AIM 5-1-6(d)(2)(f) suggests filing at least one fix per ARTCC through which the route will be flown, but this route obviously doesn't.
Have I misinterpreted the AIM or has there lately been some change to flight plan filing requirements?

I'm not completely sure, but that "1 per ARTCC" suggestion may be a vestige from non-radar days. As ATC, my mindset is: if there's an LOA routing to comply with, I do so; if there isn't, I'll clear you as filed. And on that note, I'm fairly certain that the "as cleared" feature has very limited feedback from the operation... if someone gets a reroute halfway down the line, that isn't reflected in the data.

This is a holdover from the old HOST computer system that was installed in all enroute air traffic control facilities (ARTCC's) in the mid-70's. The original code was written in just 16MB of RAM. All flight plan processing is done by the enroute computers.
Although the mainframes were updated twice before being replaced in the mid-2010's by ERAM (EnRoute Automation Modernization) the same core programming remained until ERAM.
The old HOST system stored fixes in and adjacent to the ARTCC airspace. Distant fixes were not generally stored. If you filed AAA-BBB and they were so distant the enroute computer didn't know the location of both airports (or fixes) it couldn't process the flight plan, requiring manual intervention by the controller to insert lat/longs to tell the computer where things are. That was the reason for one fix per ARTCC. The fixes were close enough for HOST to know their location.
In ERAM, that problem doesn't exist. ERAM knows all fixes in the US, and many internationally. If you file KJFK..KLAX, ERAM will process the flight plan without error. It will also apply adapted departure routes and adapted arrival routes, which means that you probably won't get that direct non-stop routing that you requested between two busy international airports.
I can't tell you to ignore the AIM, but if you do file direct, I don't think anyone will say anything about it.


text:
How to compute quaternions from raw IMU and magnetometer data?
I have raw accelerometer data (w_ib^b) and magnetometer data from a UAV test flight. I would like to reconstruct the quaternion dynamics of the UAV without accumulating error from integration.
The method I was using involves solving the following integration: d(q_b^w)/dt = 0.5*Omega(w_ib^b)*q, where Omega(w_ib^b) is of the form: [-skew(w_ib^b) w_ib^b; -w_ib^b' 0].
I was wondering whether there was an alternative method of computing the aircraft attitude given raw angular velocity and magnetometer information from a UAV?

I think this is of topic here. Other than coming from a UAV, this is more suited to mathematics.se or physics.se.

It's flight dynamics. Quaternions are used to work out the position and attitude of aircraft in earth reference axes. Euler angles are more intuitive, but if the aircraft is pointing straight up the Euler angles are undefined and quaternions are the only solution.

If all equations are digitally computed multiple times per second, all variables are updated at every frame and the integration error is only one time-step old. Full Flight Simulators use four sets of quaternions to compute the state of the aircraft in earth reference frame. To illustrate how it is done in FFS flight dynamics, here is a partial set of the steps that take place:
$$ \dot{E_1} = 0.5 \cdot (-E_4 \cdot p - E_3 \cdot q - E_2 \cdot r) + E_1 \cdot C_Q * C_{Q\Delta t}\tag{1}$$
$$ E_1 = \dot{E_1} * \Delta t \tag{2}$$
$$ \Sigma E^2 = {E_1}^2 + {E_2}^2 + {E_3}^2 + {E_4}^2 \tag{3}$$
$$ C_Q = 1 - \Sigma E^2 \tag{4}$$
$$ E_{1P} = E_1 * \frac {1}{\sqrt{\Sigma E^2} } \tag{5}$$

Equation (1) is one of four equations for $\dot{E_1}, \dot{E_2}, \dot{E_3}, \dot{E_4}$, while $p,q,r$ are aircraft roll, pitch, yaw rates.
$C_Q$ is a quaternion correction factor which uses the sum of all quaternions squared.
$C_{Q\Delta t}$ is a timing correction factor and should be less than the iteration rate in Hz. A constant value is empirically chosen that gives good stability.
Equation (2) is a simple Euler integrator using the actual time step of the computation frame. So if we're computing at 1000 Hz, $\Delta t$ = 0.001.
$ E_{1P}$ is the prime quaternion substituted in the transformation matrix from body to earth axes.

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text:
Are retired airline pilots allowed and able to help in an emergency situation?
My dad is a pilot who flew over 15000 hours in 777.
Will he be able/allowed to help the crews if the same plane is in emergency?

This quesion is much too broad to be answered. Which type of emergency are we talking about? Are your dad on the plane or on the ground? Does he know there is something going on? Does the crew know that he is a pilot? And even if we had the answer to all these questions, any answer would probably be mostly opinion based.

could be a partial duplicate of this: https://aviation.stackexchange.com/questions/163/1467

Your father could had answered this: It is up to the discretion of the pilot in command.

@mins What do you mean by "general laws"? The only laws that are relevant are those pertaining to aviation, the very subject of this site.

There's an interview on YouTube with a B-1B pilot that was asked to assist the first officer after the captain became incapacitated.

United 232 might be close to what you're thinking about: a United flight training instructor on board helped the pilots to land the aircraft, although he wasn't retired. But for this scenario to happen you need a fairly specific combination of circumstances:

The passengers have to know there's an emergency
Your father has to believe he could help significantly
The cabin crew have to decide it's worth passing your father's offer to the pilots
The pilots have to decide it's worth bringing another, unknown pilot into the situation

The basic question would be: is your father's help going to be important enough that it's worth increasing the communication and CRM workload for the crew? That's not necessarily an easy decision to make, especially if time is very limited or the nature of the emergency isn't clear.
Being "allowed" to help isn't really a consideration here, by the way: pilots have very broad emergency authority to do whatever they think is best.
Overall, it's certainly possible and it would be the pilot in command's decision to accept your father's offer or not. It's just very, very unlikely.

Reference FAR 91.3, the emergency authority of the pilot in command: "The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft." If the PIC wants someone's help, the PIC may get that person's help. (If the Captain is disabled or otherwise unable to perform the appropriate duties, the then-acting PIC would make the decision.)

There are two questions here: will he be able and will he be allowed.
Will he be able to help? Generally yes. The retired pilot's ability to improve the situation depends on a few factors, such as how long has he been not flying, his mental and physical condition, any disparities between the model which he flown years ago and the current model, updated airport locations which he may not know etc.
Will he be allowed to help? Again, generally yes, but it is the decision of the pilot in command (or whoever is in charge if the PIC is unconscious). The cockpit only has so much space, and if it is decided that the pilots on duty can handle the situation already, there is no reason to bring onboard a retired pilot from the passenger cabin. Or, perhaps he is known to the flight crew as a past coworker of the airline, and the pilots may wish to listen to the view of an experienced captain.
To conclude: it depends, with a generally yes.

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text:
What is the minimum altitude for dumping fuel?
In this question, a comment mentioned that if a 4-engine airliner suffers a 3-engine failure shortly after takeoff, the only way to stay aloft may be to dump fuel.
What is the minimum altitude which fuel dumping is possible? Possible here means, the fuel will not cause a hazard to the airplane or anyone on the ground.
Is the altitude MSL or AGL? (i.e., is it "it takes 2,000 feet for the fuel to fall before it evaporates", or "the atmosphere pressure at 8,000 feet makes fuel evaporate a lot quicker, so you can do that if you're at 8,000 pressure altitude even if the ground elevation is 7,000 feet"?)

@mins the "physical possible" altitude, not the regulations

FWIW, I can pretty much guarantee you that if a 4-engine airliner suffers a 3-engine failure shortly after takeoff, they'll start dumping fuel immediately without regard to their altitude.

A mist of partially vaporized fuel is much better for the health of the surface dwellers than would be the burning wreckage of a heavy or super heavy.

You may read a lot of interesting details on this booklet for Zurich area, where altitude (6,000 ft, but usually at 15,000 if possible) is regulated when time allows for a clean dumping. Note that fuel dumped this way is still oxidized into water and C02.

The altitude appears to be above ground level. From FAA Order JO 7110.65W Air Traffic Control:

Section 4. Fuel Dumping
9−4−3. ALTITUDE ASSIGNMENT
If an aircraft is dumping fuel in IFR conditions, assign an altitude at least 2,000 feet above the highest obstacle within 5 miles of the route or pattern being flown.

The wording says 'above the highest obstacle', indicating AGL. The CAA Manual of Air Traffic Services is much more explicit:

13.3 Controllers are to recommend to flight crew that jettisoning of fuel should be carried out above 10,000 feet agl. Exceptionally, if fuel dumping at this level, or over water, is operationally impracticable or inconsistent with safety, fuel may be jettisoned above 7000 feet agl in winter and above 4000 feet agl in summer.

This indicates that the altitude requirement of dumping fuel is from the from the first consideration i.e. it takes x feet for the fuel to fall before it evaporates. Swiss regulations go into this at a little bit of detail.

Generally, air masses are only moved vertically very slowly, usually at a settling rate of approximately 60 centimetres per second. In addition the upper limit of the planetary boundary layer (PBL) at the altitude of
approximately 3000 ft over ground renders the air flow from the upper to the lower layers more difficult. Therefore the chance that even a small quantity of fuel reaches the ground is estimated to be unlikely.

Again, it says 'above ground' indicating AGL.


text:
What is the vocabulary used by fighter pilots used to communicate?
As far as I understand, fighter pilots or more general military aircrews will use a dedicated phraseology to communicate with each other, which is different to communicating to ATC.
Is this phraseology standardized across different air-forces or even within NATO?
Are there any public documents on this phraseology?

There are NATO standard terms.  For example the MiG-29 is known as a "Fulcrum." That's not the Russian name for it but the "NATO reporting name" which you can look up on Wikipedia.
There are also some standard (but not codified) terms such as "angels" meaning "thousands of feet."  And there are some standard terms such as "bent" meaning "inoperative" but I don't know how much those are used any more.
Within a certain operating area or task force, there may be specific code words used that may change from day to day.  These would not be known to anyone outside that area or task force.

Although I come from Russia, which was previously an opposing force), let me add to your answer.
Generally nicknames for military aircraft were designed so that first letter describes is type.
Fulcrum, Fencer, Foxbat are fighters, Archer is a ground attack airplane, and so on. The same doesn't apply to some American airplanes, Hornet, Tomcat, would start from "F" otherwise.
Also there are some terms, such as "spike", denoting radar irradiation, "bogies" - enemy aircraft.

@Eugene that system only applies to the NATO reporting naming system for Soviet aircraft, not to anything else. It was created to have an unambiguous naming system for enemy aircraft when the actual names weren't known or too hard to pronounce.

@jwenting You are right! And also when no clear communication is possible first letter helps with type understanding.

When I read this question, I think of the chit chat which goes on during sorties.  It IS non-standard, and varies by location and service.  On youtube there is a recording of a F-4D pilot who went into the drink at night in the North Sea.

Listen to that (long) recording. The dialog is quite similar to the dialog used, for example, by pilots in Vietnam. (A buddy of mine was base commander of the affected pilots.)
You may find more current examples from more current conflicts where there are videos with radio audio. Much of the terminology is not standardized, but there are certainly components which are.
An example of terminology which is rather universal but perhaps not standardized, might be the term "feet wet" which means the flight has crossed the shoreline and is over water.

They use brevity codes. They are used to quickly convey information on the radio. Like all things military, they are standardized but they do have some variation between services. You can find a list of US/NATO multi-service codes on Wikipedia.


text:
Are there schools that would hire a non-CFI ground instructor?
Do flight schools have a strong preference for the CFIs giving BOTH ground and flight instructions? Would there be any interest on the part of some schools to have a pilot, but not a CFI do the ground teaching, while their CIFs would be entirely dedicated to the flight instruction?
I am a newly minted PPL and I would love to associate myself with some flight school and teach the ground as a Certified Ground Instructor. First, it would be really fun to teach this stuff, but also I hope that I could get some financial break on getting my instrument rating (i.e. the highest level of certification I’m interested in). I’d be also interested in staying with a school longer on a more permanent basis (unlike airline-bound CFIs)

With the shortage of CFIs now would be the time.  And, yes, know of at least one school doing this.

Our local flight school had a dedicated AGI/IGI for a while. Lots of CFIs don”t like doing ground instruction and, if they are building hours, every hour on the ground is an hour they are not building time. I like teaching and so I just took and passed all three tests and need to fly over to a FSDO to get my certificate.
For the Fundamentals of Instruction Knowledge Test, study the Gleim book. If you have time, and if you want to be a CFI, at some point you will need to read FAA-H-8083-9A Aviation Instructor's Handbook but you don’t need to read it to pass the exam. A lot of the information in the book is wrong, so I had a hard time memorizing the wrong answer to questions. You probably won’t have to worry about that.
For the IGI and AGI it probably helps to read FAA books or whatever you prefer for getting your aviation knowledge. And you definitely need to study FAR 61 and 91 and know the VFR and IFR charts. I used the Gleim books Flight/Ground Instructor and Instrument Pilot and there were only a few questions that were completely new to me.
I’d say that about half of the questions are really stupid. e.g.
The force acting opposite of lift is:
A. Apples
B. Gravity
C. Oranges
Another quarter were interpolation/math questions that you will never ever need while flying. The study guides do a good job preparing you for them. The trick is to read the question really carefully. e.g. Are they asking you to look on the chart for landing distance or do you need to do another calculation to get ground roll.
There are a bunch of E6B questions that you just need to be really careful in your arithmetic and reading the question.
There are a few that I really had no idea what the question was, let alone what the right answer was. I got about half of those right. There were also a couple on each test where none of the answers was the correct answer.
I took the Commercial and CFI since they are good for two years and I won’t have to study them again if I decide to get a CFI.
My results: FOI 84%, AGI 88%, IGI 90%, CFI 87%, COM 92%.
I studied for a month, which was a bit of overkill.
Sporty’s and King Schools let you take practice tests for free. I put a lot of my notes up on my website so you can save time when studying by printing and memorizing them.

"The force acting opposite of lift is: A. Apples B. Gravity C. Oranges" Is that really on the test?

They might do so if you held in advanced ground instructor (AGI) certificate.   I believe all that’s required for this is to pass both the fundamentals of instructions written test as well as a ground instructor written test in order to obtain this certificate.
Well this might be possible, it is far more useful to flight school to hire on a CFI since they’re capable of both the ground and flight instruction. It all depends on what their staffing needs are, but right now most schools are desperate for new CFIs.


text:
How does the ground effect affects longitudinal stability?
I recently learned that the ground effect increases the effective AoA of the wing and thus increases lift, how does that translates in to the tail plane and it's stabilizing effects? does it reduce/increase stability?

It should be nice if answers mention ekranoplan stability.

Ground effect makes the airplane more longitudinally stable for two reasons:

Ground effect increases the lift curve slope ($\frac{\partial{C_{L_t}}}{\partial{\alpha_t}}$) of the tailplane due to vortex reduction. An increase in tail lift curve slope is equivalent to increasing the effective tail volume.
Ground effect decreases the downwash of the wing on the tailplane (Ref. ESDU Item 72023). The reduction in the downwash slope ($\frac{\partial{\epsilon}}{\partial{\alpha}}$) again increases the effective tail volume.

Ground effect also affects the wing moment slope, but the effect is generally minor and does not follow a general trend.

It depends on general geometry of the aeroplane:

The vertical position of the main wing and the horizontal tail.
If the aeroplane even has a horizontal tail.
The sweep angle.
The angle of incidence in the landing flare.

When a wing enters ground effect, its lift coefficient rises: the wing creates more lift at a given speed and Angle of Attack. A wing is considered to be in ground effect if it is within about half wingspan distance to the ground. Since the main wing has a much larger span than the horizontal tail, it enters ground effect earlier, creating a nose up moment due to more lift on the main wing only.  Low wing aeroplanes have a more pronounced nose-up effect than high-wing aeroplanes do.
 Image source
An increased nose up angle brings the horizontal tail closer to the ground, which will enter ground effect as well at a certain point. Which will the counter the nose-up moment.
A wing with large sweep, at landing angle of incidence, will see the wing tip area enter ground effect earlier, creating a nose down moment.
Concorde enters ground effect with the wing trailing edge first, creating a nose-down moment. In flight this would be called Increased Stability, however in the landing a nose down moment may introduce nose wheel slam.


text:
What is the use of this object in the cockpit of a Bombardier Dash 8 Q400?
What is the use of this object in the  cockpit of a Bombardier Dash 8 Q400?

It is a mechanical checklist where each item on the list can be flipped to indicate that is has been checked. You can see it in operation in this YouTube video (which I believe is where you got the image from). Each of the 6 stacks can be extended to check the items and then collapsed again in order to not obstruct the pilot's view.
It is not a default part of the Dash-8 Q400. As far as I know, Qantas is the only airline using it.

Thank you dear friend


text:
What is this flange on the engine?
Flying home from the Denver ComiCon, on a 737, I saw an angled flange on the engine. Could you describe its purpose?

Photos by CGCampbell licensed CC0

See also: http://aviation.stackexchange.com/questions/5160/why-dont-all-aircraft-use-need-nacelle-chines

Good thing the photos are copyright.  You wouldn't want someone steeling those.

@kjmccarx I posted that because I improperly failed to accredit photos in another stack exchange and was flagged for copyright violation. I have cleaned up all of my questions and answers so that any photos I used are either my own, or copyright as creative commons and attributed correctly.

@CGCampbell Fair enough.  I was just giving you a hard time.  Always better to be safe than sorry.

Failure to attribute the source is not the same as claiming something as your own, or making money off it.  Have there been any legal precedents set where reposting something from the public domain without attributing it was ruled a copyright violation?

Wait, so you posted your own photo, did not attribute it as your own, and somebody claimed that was a copyright violation?!  I'm no attorney, but I am positive that falls well short of any legal standard on the issue.  I think you encountered one of the many busy-bodies on this site...

You know what? This question is 5+ years old, they're my photos, they're in the PD, I attributed them... I'm good with it.

I do not believe the teaching in the patent is correct.
Instead of the downwash from the strake suppressing the wing upwash (and remember, the other side of the vortex adds to the wing upwash!)  we believe that the vortex is well organized and can withstand the adverse pressure gradient of the wing better than the 'junk' wake of the nacelle without the strake.
The size and location of the strake determine when the vortex will burst, and hence govern when the inboard wings stalls.  Ideally you would like this to be at the same time as the outboard wing.  Too late and you get unacceptable pitch up.  Too early and you lose low speed performance (higher stall speeds equated to higher speed schedules and longer takeoff field lengths).
A side note, the outboard strake is of little to no value at all, which is why Boeing airplanes only have strakes on the inboard side.

@Dougball The answer contains valuable information. Please edit the answer so that it forms a comprehensive answer to the question.


text:
What are the following documents about aircraft maintenance?

What is a service bulletin? How does it originate?
What is a rapid revision in aircraft maintenance?
What is a non-conformation report?

What is the difference between these 3 documents?

A service bulletin is a document that the manufacturer of an aircraft issues directly to operators of related aircraft. It mandates some maintenance / replacement / check activities.
A rapid revision is a change to the maintenance documents, that is not released officially according to normal procedures, yet.
A non conformation report is any discrepancy found in the aircraft / system such that the related system does not look / operate / behave / function as expected. This document is mostly a form that the ground crew / technicians / pilots generate.
Disclaimer: these are general information and details would change depending on whether the aircraft is a civil or military one, and the certification type. This answer is written in the perspective of military aircraft, for general knowledge.

How does these change for civil aircraft?

For civil aircraft, service bulletins are mainly related to product changes that are not safety related (except for Mandatory Service Bulletins). They are changes to the systems that improve functionality, or replace parts that are obsolete, etc.

You can get details of procedures for a particular certification authority, such as FAA, EASA, from their web sites.

I will check the sites. thank you


text:
Does an instrument rating bridge category and class?
I had previously been under the impression that if a pilot held an instrument rating that it would apply to aircraft in another class.  The requirements of 61.57 would seem to support that since currency can be maintained in aircraft of the same category.
However, reading section 61.133 leads me to believe that any check ride to add a class would require an instrument checkride as well:

A person who applies for a commercial pilot certificate with an airplane category or powered-lift category rating and does not hold an instrument rating in the same category and class will be issued a commercial pilot certificate that contains the limitation, “The carriage of passengers for hire in (airplanes) (powered-lifts) on cross-country flights in excess of 50 nautical miles or at night is prohibited.” The limitation may be removed when the person satisfactorily accomplishes the requirements listed in § 61.65 of this part for an instrument rating in the same category and class of aircraft listed on the person's commercial pilot certificate.

Am I correct in this interpretation?  Are there any other CFR sections that might shed some clarity on this?  Does any class rating add-on, (presuming one wanted to exercise the option of IFR in the new class) require a full blown instrument check even if one is already instrument rated and current in a different class?
ADDENDUM:  After re-reading this almost seems self answering based on the quote I provided, but I know what sometimes regs can be interpreted differently based on other sections.  I am just incredulous that a full-blown syllabus per 61.65 would be necessary when really IFR isn't any different from Single to Multi.  Makes the upgrade that much more pricey!

If so, this may explain the option of doing multiple checkrides at once, which never made sense to me risk-wise until I saw this question.

The Airman Certification Standards for the Airplane Instrument Rating shed light on this question. There are four classes of instrument rating for airplanes and that the tasks required for each class differ:

The abbreviation(s) within parentheses immediately following a Task
refer to the category and/or class airplane appropriate to that Task.
The meaning of each abbreviation is as follows:
ASEL: Airplane – Single-Engine Land
ASES: Airplane – Single-Engine Sea
AMEL: Airplane – Multiengine Land
AMES: Airplane – Multiengine Sea
Note: When administering a test based on this ACS, the Tasks
appropriate to the class airplane (ASEL, ASES, AMEL, or AMES) used for
the test must be included in the plan of action. The absence of a
class indicates the Task is for all classes.

So your assumption is correct. You need an instrument rating in each class of airplane you wish to fly IFR. However, per §61.57 (c) (1) your   currency can be accomplished in different classes in the same category but you can’t mix and match categories e.g. 5 approaches in a SEL and 1 in a MEL is OK. 5 approaches in a SEL and 1 in a helicopter is not OK.

Do you not just need to attach a class to the instrument rating?  The instrument rating is at the category level but you must demonstrate proficiency in various classes to exercise the privileges of the IR.  You don't get an IR for each class, you get classes added to your IR.  Sounds pedantic but it is an important distinction, else a CFII would be required to train for additional ME class rating to an existing SE Comm-Inst, for example.

@acpilot I’m not sure what you are saying. In the US you have a certificate  eg Private Pilot, Commercial Pilot, or ATP. Then you have ratings added to it, eg. instrument, multi, seaplane, etc.  The Flight Instructor certificate is a separate certificate with ratings e.g. Single-engine, multi-engine, airplane instrument. So for example, a typical CFI has a commercial certificate with Airplane Single Engine Land and Instrument Airplane ratings added to their Commercial Certificate.  Their CFI certificate would have at least Airplane Single and Instrument if they are a CFII. The ACS sets rules.

The answer says you get an instrument rating in each class. You don't. The rating is for the category (ex. instrument airplane) and you demonstrate proficiency in each class to exercise instrument priviliges.  OP reads the reg incorrectly; once the instrument rating in category is earned, it's earned. ACS simply tells the examiner what must be observed in order to authorize instrument privileges for an additional class.  Please correct me if my understanding is incorrect.

@acpilot I think we are saying the same thing. You earn an instrument rating in a category and class of aircraft. I have a Private Pilot Certificate. My instrument rating is for SEL on my certificate. I do not have an instrument rating for Multi-Engine Land. To add a MEL rating to my Private Pilot Certificate, I must complete portions of the ACS for that Class of aircraft. (No need to take the written again.) Look up some CFIs in the FAA database. You’ll see that they have a Commercial Certificate and an Instrument rating. If they have a more than SEL it will list additional ratings they have.

The IR is category only.  There is no such thing as a single engine land instrument rating or multi-engine sea instrument rating, just instrument airplane (or helicopter, etc).  You get an IR in the category and then demonstrate proficiency by class.  Failure to demonstrate proficiency on a class add-on leaves a pilot with a VFR only restriction for that class.  61.65 specifies nstrument rating aero experience for the category level only.


text:
What sort of briefing and planning information would an airline pilot in the 1960-70s have used?
Slightly related: Do airliners get substantially different weather briefings from the rest of us?
Highly related: How was the navigation managed on jetliners before having programmable routes?
Highly related: How long does flight planning take / when is it done / how is it done?

In the modern day, the tasks of an airline pilot preparing for a cross-country1 flight are very different from the tasks of a private pilot preparing for a flight.  The private pilot may look at a sectional, decide on a destination, choose landmarks, and look up frequencies. Whereas the airline pilot is assigned a destination, receives a briefing package from dispatch, and verifies the correctness of the route.
My question is, was it always this way?  For example, in the early days of the jet age, what sort of flight planning and briefing might the average airline pilot have done? Would they have decided on routes day-by-day?  Would they have calculated time/fuel/distance for each leg by hand the way some private pilots still do2?  To what extent would dispatchers be involved in the process?
I doubt many historical examples of actual training materials for flight planning exist, but they would make a spectacular answer to this question.

1 Which, really, is almost any airline flight.
2 (Or maybe not. Ah ForeFlight, the great equalizer...)

@ymb1 - Oooh, good one!  Highly related.

You're talking about an era where there was a dedicated engineer for that, the 3rd crew person, who managed engines, fuel, route, navaids, weather...

@ymb: For example, the B707 which started to fly in the late 50s had a navigator.

@ymb1. I'm reading an article (in French), where the number of OMN (this is the name for the flight engineer in France) was more than 1,600 in the 70s/80s, in France. B747-200/300 were still flown at 3 in 2000.

There is lots of info here I will go back a bit further before the 60's for a complete answer. Dedicated flight dispatchers date back as far as 1936 when they were broken off from ATC duties into their own functionality.
Weather planning involving ground based observations and intercommunication dates back as early as the 1930's when the technology made inter-airport communications possible and subsequently en-route weather planning possible before takeoff.

In 1930, Boeing Air Transport installed the Western Electric
radiotelephone system in its aircraft and 18 ground stations. Ad copy
for Western Electric Aviation Communication Systems referred to Boeing
Air Transport pilots as “always in touch with dispatchers and weather
observers along their routes. Reports on weather and field conditions,
guiding radio beacon signals, or instructions come in clearly, helping
pilots to bring their ships through on time”

Formal dispatch training goes back to at least 1936 and had various requirements. There is some great footage from a 1947 film about the "flight superintendent" here (at 4:55) you should watch.

The first documented educational program for training aircraft
dispatchers appeared in the October 1936 issue of Aviation. The
subjects covered included meteorology, dispatch practice, and airline
operations. The course took 18 months to complete and required 2 years
of college or 9 months of accredited engineering college coursework
prior to enrolling (p. 66). The 1947 vocational film Your Life Work
Series: Air Transportation called the dispatcher a “flight
superintendent.” The film describes a flight superintendent’s key role
in all flight operations: "He is the man who decides whether the
planes will fly or not. He releases all planes on his division,
follows their progress in the air, and keeps the captains…advised of
conditions affecting their flight…He coordinates all flight operations
to achieve these objectives: safe, swift, and dependable air
transportation." (Twogood, 1947) The flight superintendent position
required a pilot certificate and a dispatcher certificate issued by
the Civil Aeronautics Authority (Twogood, 1947).

En-route pilot reports (PIREPS) date back to Feb 1 1943 so pilots would have had access to real time conditions over the radio from ground based stations going back well before the 60's allowing pilots to make en-route weather choices and ground dispatches to make pre-flight choices.

Feb 1, 1943: CAA inaugurated an expanded flight advisory service at
all air route traffic control centers. The centers originated
advisories on weather changes and hazardous conditions, and airway
communication stations relayed this information to nonscheduled
pilots. The service provided these pilots with some of the assistance
that airline pilots received from their dispatchers. In Jul 1943,
CAA's communication stations also began a flight communications
service. When contacting pilots by radio, communicators were
instructed to volunteer information on important weather changes or
inoperative facilities along their route.

This copy of Aviation Weather dates to 1975 (and is pretty neat) but the preface indicates that its publication goes back as far as '43 indicating dedicated weather information was published going back at least that far (a copy can be had if you really want).
Thunderstorm avoidance was (and still is) a big issue. A good set of MK-1 Eyeballs is always your first option but on board radar tests date back as early as 1949 with the first units coming around a decade later Which would allow pilots to offer far more accurate PIREPS

Since the advent of commercial aviation, thunderstorms caused delays,
diversions, and accidents. Airlines attempted to find ways to avoid
enroute weather while maintaining scheduled operations. In 1949,
American Airlines and the Unites States Navy conducted tests of an
onboard weather radar system installed in a Convair airliner (“Flying
Lab,” 1949, p. 28). In 1956, American Airlines equipped its fleet of
DC-7s with airborne weather radar (“AA to Equip,” 1955, p. 20).
Airlines quickly embraced the innovative technology, and Aviation Week
(Christian, 1955) quoted a Northwest Airlines pilot: “We all wonder
how we ever got along without it. Pretty soon the public won’t fly in
anything but radar-equipped airplanes” (Christian, 1955, p. 40).

The tricky part becomes trans-oceanic flights where there may not be any reporting stations. The importance of trans ocean (Atlantic) weather reporting became important during WWII and the use of light/weather ships became apparent to gain such information. Transatlantic flights would not have been in the dark about weather on account of that.
Here is a pretty neat article about the radios they used to actually make the reports from ground to the aircrafts.
As noted in the comments many airplanes of the era had a Flight Navigator on board, they would have provided a great deal of fuel and navigational planning as that was their job. The FAA still has a handbook covering the tasks of the navigator you can find here.

On any note: Numerical weather forecasting dates back to the turn of the century and by 1950 the national weather service was providing future outlooks forecasts. Paired with airport based reports, PIREPS, and onboard radar systems for more in flight information; Trained dispatchers were capable of making educated decisions on flight dispatching. In some cases these dispatchers were full time employees of the airlines and much like in todays era dispatchers would have been responsible for weather planning and likely en-route planning as well as fuel requirements with final checks landing on the plate of the flight navigator.


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Does using a Starlink mini in a plane's cabin pose any danger to the plane?
Does using a Starlink mini in a plane's cabin pose any danger to the plane? I am mostly interested in commercial planes.

https://aviation.stackexchange.com/questions/2021/why-arent-cell-phones-allowed-to-be-used-in-aircraft

Why do you think there is more than zero danger?

You'd likely have problems picking up a signal inside the cabin.  That's why the airplane's Starlink antenna is mounted on the outside.

@MichaelHall Thanks, good point: I've added Would a Starlink mini placed inside a plane's cabin be able to get Internet connection? to focus on that aspect.

In short
This transceiver could be dangerous aboard an aircraft, not because of its 4W transmitter but because the antenna is a hi-gain antenna concentrating this small power within a narrow cone of 3.5°, where it has the same effect as if it were a huge 6.6kW equally distributed.
However this is only a possibility as the transceiver is likely prevented to transmit without the satellite in sight, i.e. when the antenna is not pointed outside. When the bean is targeting a satellite, the level of radiations in other directions is unlikely to interfere with avionics.

The Starlink transceiver itself
When the transceiver is powered, there are different points to consider:

The device uplink transmitter works in Ku band at about 14GHz. The RF amplifier maximum power of a Starlink transceiver, specified in the FCC license request, is 4W. This seems to be the same as the maximum EIRP power of an old 2G/GSM-1800 cell phone. However this comparison is misleading, the two power numbers are not comparable:

RF power is measured in the RF amplifier, before the antenna.

EIRP power is the one effectively radiated by the antenna in the beam direction.

EIRP power is the product of the RF power by the antenna gain. The flat array antenna has a theoretical gain of 35dBi (calculated here as 32.8dBd which is the same, comparable antenna). It is a beamforming device, steering and concentrating the power in a cone of 3.5° centered on the satellite direction:

4W is 6 dBW (I use this dB converter)
Adding the gain 35dBi gives 41dBi
41 dBi is more than 12kW, but half this power (3dB) is lost in the system
This gives 6.6kW EIRP. This is a lot and definitely not comparable to the 4W EIRP of a GSM cell phone.

The Ku band 12GHz downlink receiver also radiates spurious signals on unknown frequencies, depending on its technology. One cannot evaluate this point easily.

The Wi-Fi access point transmits on the Wi-Fi bands with an EIRP of 100mW on 2.4GHz and 200mW on 5GHz, this is not a concern.

Equipment resistance to interferences, including avionics
Reading research documents on PED alleged interference with avionics, you see FCC and FAA (see below) have adopted this position: Usual PED are a priori innocuous for avionics equipment. This is based on the fact all commercial products can be approved only if they satisfy some obligations:

They mustn't radiate more than a small level of spurious signals or harmonics.

They must be able to work with spurious signals from other devices, limited in power as stated above.

They must be able to cope with other approved devices using their maximum approved power.

Operator rules for usual PED
PED rules are mostly operators rules, the regulator provides a guidance to establish the rules, this guidance is mostly asking for a test before allowing unusual equipment use aboard.
Usually operators forbid using the device during the critical phases (when the PED light is on), and allow them in cruise. However a hi-gain antenna is not a usual equipment.
Hi-gain antenna case
Both Starlink devices and avionics devices are approved as meeting the interference obligations. Starlink lists these obligations:

Therefore, Starlink’s in-motion operations, including for vessels, must accept any interference received from both current and future services authorized in the band – even if such interference causes undesirable operations for Starlink Services and its customers. Starlink in-motion Services must not cause harmful interference to any authorized service in the band, whether licensed or not.

However the unusual hi-gain antenna would require a dedicated test by the operator before allowing its use. This is unlikely this test has been already conducted.
You can compare a gain antenna with a laser light: Even with a limited power, the light beam can dangerous due to the small size of the beam. Similarly, you cannot guarantee the antenna panel will be directed to the outside, a configuration where only a small signal, likely acceptable, is directed to the avionics.
The way the array works is not fully described. However to meet power density constraints protecting GSO (geostationary) satellites from the signals of the lower NGSO (non-GSO) satellites, NGSO user equipment uses approved EIRP masks (in license request), it is likely the user transmitter won't transmit at a significant level before it finds the direction of the NGSO satellite currently covering its cell, hence it may be prevented to transmit when not pointed to the outside of the aircraft. That's likely, but still a a supposition.
The crew may not be familiar with amplifier power and EIRP difference. For my own safety and the safety of others, I would ask both Starlink customer service and the operator before using the device within an aircraft.
FAA and FCC view on PED in 2013: No restriction a priori
A 2013 FAA document, now cancelled, summarized the regulation:

FCC doesn't prohibit the use of PED, including transmitters, including during critical phases of flight.

FAA doesn't prohibit it either, and it ready to help operators to test PED. In the end it says PED rules must be defined by each operator.

From FAA Notice 8900.240, Recommendations on Expanding the Use of Portable Electronic Devices During Flight, 2013:

Under the current regulatory environment, the operator is still responsible for determining which PEDs may be used on its airplanes. Each operator’s PED policy determines what types of devices may be used during which phase(s) of flight. Crewmembers are responsible for ensuring passenger compliance with an airplane operator’s PED policy. Current guidance allows broad use of non-transmitting PEDs during non-critical phases of flight without detailed study of specific PEDs.

However, if an operator wishes to expand its PED use allowance, FAA policy and guidance is in place to allow PED use, with the proper testing and analysis, during any phase of flight.

Operators have been hesitant to deviate from current FAA guidance, as there has been no clear direction on methods to demonstrate an equivalent level of safety when expanding PED use into critical phases of flight.

FCC regulations also govern certain aspects of PED usage. The FCC has established rules for radio transmitters and consumer electronics to minimize the risk of harmful interference to other users of the airwaves. FCC rules, with a few notable exceptions, do not prohibit use of radio
transmitters or consumer electronics aboard airplanes.

As of 2013 several studies, including by NASA, had already analyzed many events where PED were suspected to cause critical avionics problems (like in Personal Electronic Devices and Their Interference With Aircraft Systems from 2001), still FCC/FAA didn't see any problems allowing their use in fight, after a test. This document was likely replaced and amended, but I cannot find a current equivalent, so it is safer to ignore the conclusion.

Smartphones contain batteries, and batteries sometimes catch fire.  Occasionally that happens on a plane.  Cabin crew know how to put the fire out.
Starlink Mini has a power supply that would need to be plugged in.  There is no battery.  So it's not likely to have a battery fire.
The Starlink Mini is over 6 kg, so it would do a lot more damage than a smartphone if you drop it on the pilot's toes when they walk by.

Thanks, the Starlink Mini is 1.1 kg. (https://www.starlink.com/specifications?spec=5). Still painful though :) you forgot head injuries when I'll brandish it to try to get a signal.


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What are the differences, if any, between aviation custom earplug and regular custom sleeping or musician earplugs?
I see some websites selling aviation custom earplugs. What are the differences, if any, between aviation custom earplugs and regular custom  sleeping or custom musician earplugs (i.e., flat-response attenuators)?

Could there be an issue of needing to relieve air pressure differences when climbing or descending?  Putting an airtight thing into your ear doesn't seem like a great idea in the aviation context-- wouldn't pertain to open-cell foam earplugs but might pertain to some others--

Aviation earplugs for use in piston engine airplanes needs to attenuate frequencies under 200Hz, because both the engine exhaust and the propeller wash pulse hitting the windshield are in the range of 70Hz for a 2 blade, 4 cyl engine, and a little over 100 Hz for a six cylinder with a 3 blade prop, or some mix of the two, so these are the dominant frequencies. The rest is white noise from the air stream.
This requires the earplugs to have mass to them, as foam earplugs have relatively little low frequency attenuation. There is a brand called Isolate Earplugs that use a metal cylinder, aluminum or titanium, with a foam rubber tip, which gives it mass. So look for earplugs with that feature. Isolates work well but they are about 40$ per set.
I make home-made ones by wrapping golf club ballast tape (lead sticky tape) around the shaft of a 3M Push-In earplug, and covering the tape with heat shrink tubing. If you don't like the idea of lead tape in your ear, even if its hidden under a sleeve of heat shrink plastic, you could use some other foil material, with somewhat less performance, but still better than foam earplugs. In left to right in-ear testing using headphones with a low frequency tone at high volume, my homemade ones performed better than even the Isolates.


text:
Was the Yeti Airlines Flight 691 crash the first time a commercial airline crash was livestreamed from a plane?
The Yeti Airlines Flight 691 crash that happened on 2023-01-15 was livestreamed by a passenger in the plane. Was the Yeti Airlines Flight 691 crash the first time a commercial airline crash was livestreamed from a plane?

Not an answer but a note: while most major news reports are stating that the video in question is genuine (https://www.bbc.com/news/world-asia-india-64287331) the usually-aviation-authoritative AvHerald currently has taken the opposite view (https://avherald.com/h?article=503c63e9&opt=0).


text:
Why build a sturdy embankment at the end of a runway if there isn't much to protect beyond it?
I read on the Wikipedia page about the Jeju Air Flight 2216 crash today:

The aircraft overshot the runway and struck an embankment holding the ILS array while attempting a belly landing after its front landing gear failed to deploy at Muan International Airport

What's the point of making that embankment so sturdy? The plane was landing fine (source) before it hits the embankment and on Google Maps I don't see much to protect behind aside maybe a few unlucky cars.

Source: Google Street.
More generally, why add a sturdy embankment at the end of a runway if there's not much to protect behind?

Overview of the end of the runway:

Image source: Sky News on YouTube.

This thread is approaching the point of speculating about an accident, and has been locked to avoid further devolution in that direction.

This answer is an attempt to gather facts and references to inform on ICAO standards and how they might be applicable to the context. Elements might be wrong or incomplete, and cannot be used to draw any conclusion. Drawing conclusions is the mission given to the ARAIB investigation team, it will take months to collect facts and conclude.

Accident circumstances
The aircraft landed on RWY 19, following a southward course. From ASN:

Jeju Air Flight JC2216, a Boeing 737-800 registered HL8088, was involved in an accident at Muan International Airport (MWX/RKJB), South Korea. The aircraft made a gear-up landing on runway 19. It slid pas the end of the runway and collided with the ILS localizer antenna array and a wall. [...] MWX runway 19 has a Landing Distance Available (LDA) of 2800 m.

From the airport instrument procedures, the runway and the location of the south berm supporting the localizer antennas:

Localizer berm
The IMAN localizer, used for a precision approach of category I, is located south of RWY 19 beyond the runway end. The antennas are placed on top of a berm. From Google Street View, berm seen from the west side:

ICAO standards
ICAO is a UN agency for the facilitation of international aviation. Almost all countries have signed the Chicago Convention and are part of ICAO.
ICAO States members design, publish and update common standards and recommendations, in the form of Annexes to the Convention. Annexes referenced in the answer are mostly Annex 10 (navigational aids) and 14 (airports). Korea uses ICAO standards for its international airports. You can read more in:

Do all International airports need to be certified by ICAO?

Standards applicable to localizer support

Why adding a sturdy embankment at the end of a runway if there's not much to protect behind?

The embankment isn't for protection. The south end of the landing strip is about 6 m below the north end. The berm is to raise the localizer array.

Source (modified).
This additional height was likely necessary to meet the beam requirements in Annex 10 (e.g. range and phase linearity).
A similar accident occurred in 2004, at Halifax in Canada: An overloaded freighter, a Boeing 747-244SF, missed its takeoff and hit an earthen berm supporting the localizer array (investigation report).
ICAO defines a runway end safety area (RESA), which must be as extended as possible, with a minimum required of 90 m from the runway strip.
In the Halifax accident, the investigation team determined the berm wasn't part of the RESA and thus was allowed. The investigators noted there were similar berms at different airports in Canada.
In 2013 Korea proposed to extend the RESA from 90 m to 240 m for long runways. The most recent edition of Annex 14 publicly accessible is dated 2022. It includes a recommendation (not a standard):

3.5.4 Recommendation.— A runway end safety area should, as far as practicable, extend from the end of a runway strip to a distance of at least: 240 m where the code number is 3 or 4 [...].

At Muan, the runway has a code number 4 (minimum takeoff distance 1,800 m and over).
Current frangibility requirements for obstacles
Frangibility requirements extend past the RESA 90 m, in particular for navigation equipment like a localizer. In 2022 edition of ICAO Annex 14, the reference for aerodrome design:

9.9.5 Any equipment or installation required for air navigation or for aircraft safety purposes which must be located on or near a strip of a precision approach runway category I, II or III and which: a) is situated within 240 m from the end of the strip [...] shall be frangible and mounted as low as possible.

Doc 9157 Aerodrome Design Manual, Part 6, Frangibility (2006), which is a technical manual detailing Annex 14 specifications, mentions about the previous specification:

1.3.4 Annex 14, Volume I, Chapter 9, also specifies that any equipment or installation required for air navigation purposes which must be located on or near a strip of a precision approach runway category I, II or III and which: a) is situated within 240 m from the end of the strip and [...] should be frangible and mounted as low as possible.

Note one document uses must, the other should. It can be an indication this specification has changed from a recommendation in 2006 to a standard in 2022. Another possibility is this matter is more complex than I can see, and my view is actually incomplete. In addition, nothing indicates airports must be partially redesigned when the standards change.
Definition of the runway strip (Annex 14):

3.4.2 A strip shall extend before the threshold and beyond the end of the runway or stopway for a distance of at least: [...] 60 m.

A stopway is an area which can be used in case of overrun after landing or aborted takeoff. The existing area on each end of Muan runway is not a stopway, it's a clearway, an obstacle-free area for the safety of the takeoff. In this case, the runway strip extends 60 m beyond the threshold. The strip is depicted as a dotted rectangle on the airport diagram.
The frangibility is thus recommended (or required, as explained above) on a distance of 60+240 = 300 m beyond the threshold.
Muan runway strip at the south, with corresponding distances (magenta line is 300 m long):

Source: Google Satellite XYZ tile server (modified), distances are ellipsoidal (EPSG:3857).
The distance of 240 m extends past the localizer. This tends to indicate the localizer should be concerned by the frangibility specification. However remember we don't know if the applicable items are recommendations or standards. I'm personally doubtful Korean engineers and the certification team would have made a mistake when assessing this aspect, so don't draw hasty conclusions.
Runway excursion events
Regardless of whether the berm at Muan was compliant with applicable ICAO standards, the question about whether it should be allowed by ICAO standards is legitimate, but the answer is not straightforward, some food for thought:

Regulations cannot be based on very rare events, even catastrophic, that's not specific to aviation. Neither carriers nor travelers are able to pay for "total" safety, flying is inherently hazardous. Compromises must be found when agreeing on airport design specifications at worldwide level.

Specifications are adjusted, sometimes changed in depth after incidents and accidents. Investigation reports always draw lessons from what happened, to ensure what was supposed to be rare isn't actually more frequent than initially evaluated.

Statistics are gathered by different organizations. E.g. we know there are about 10 runway excursion events a year worldwide for commercial aircraft. This is the second cause of all accidents.

IATA, the syndicate for commercial carriers, publishes an annual detailed report on safety, with an analysis of the factors contributing to accidents. One of their standard cause is Inadequate overrun area, trench, ditch, proximity of structures.

From a IATA report for 2015 accidents (I've no access to a more recent one), there has been 68 accidents worldwide. Inadequate overrun area, trench, ditch, proximity of structures was a contributing factor for only 2% of the accidents, this was the least contributing factor to accidents. If a localizer was involved, it would have been in this class of contributing factors.

Localizer at ground level
For comparison a regular localizer array at ground level (source):

References

Muan Airport diagram.
All ICAO Annexes
ICAO Annex 10 volume I (navaids, pdf)
ICAO Annex 13 (accident investigation, pdf), used for ARAIB.
ICAO Annex 14 volume I (aerodromes, pdf)
ICAO Documents associated with Annex 14.

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In this particular case, the embankment wasn't built to protect anything, only to raise the ILS array so that it can function.
Generally, airport walls and embankments are not built to protect something behind them, but primarily to protect the aircraft. You wouldn't want cars, people, animals, or anything else from the outside to randomly venture onto the runway.
And for an aircraft that has overrun the runway, it's sometimes safer to crash into a barrier than to keep going past it - same principle as traffic barriers. It's not always safer, it's not always a good decision, but it's not without rationale.
Muan airport (MWX) in particular has public roads followed by water on both ends of its runway. It's not great placement for an airport safety-wise; ideally, you'd want flat empty plains on both ends. But safety in the event of a crash is rarely among the top concerns when picking the spot for a new airport, especially in space-restricted countries such as Korea. It's mitigated after the placement is decided upon.
Seawater generally isn't considered a safe surface - it can be better than hard surface in some crashes, particularly belly landings, but greatly complicates any emergency assistance. So, overall, one wouldn't deliberately design an airport for runway overrun to go into the ocean, even if it often ends up being the case. In this case, raised ILS placement was a technical requirement, and since the terrain past the runway is dangerous anyway, it likely wasn't considered a big safety compromise.
It's possible to make runway overrun incidents safer. ICAO recommends extending runway safety areas as far as practicable. EMAS or Engineering Material Arresting System - basically, a bed of foamed concrete - is a major improvement, helping with malfunctioning brakes and wheels-up landings. It's mandatory when a minimum runway safety area cannot be provided, but not otherwise, though studies show that EMAS have globally saved more money than they have cost to build.
In Muan's case, the runway safety area complies with the 300 ft minimum, but not with the preferred 1,000. The line of thinking that drives such decisions is that you keep the RSA safe, and if it's not enough, it's too late. But there's a lot of airports with unsafe overrun areas around the world. It can be buildings, highways, cliff dropoffs. MWX is not the worst. Minimalist airport design with water on one end and buildings on the other is pretty common in coastal areas.
In hindsight, it was a bad decision to build the ILS localizer on a raised embankment, rather than level the ground more smoothly or design a taller collapsible metal structure for it. But it's not exceptional; past the RSA, all bets are off. A number of planes have crashed into airport buildings after a failed takeoff or landing, which could have been avoided, had these buildings been built off-axis from the runway.

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According to two experts on Sky News in 2 independent interviews, there shouldn't be a sturdy embankment at the end of a runway.

You would not normally have a heavy duty concrete wall in the overrun area at the end of the runway.

(Name of the expert in this interview:
Former airline pilot Terry Tozer http://www.terrytozer.co.uk/)

That kind of structure [the embarkment] shouldn't be there.

(Name of the expert in this interview:
David Learmount https://davidlearmount.com/about/)

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Why are there 6 airports that straddle the Canada–US border?
I read on the Wikipedia page for the Avey Field State/Laurier Airport:

Also known as Avey Field State/Laurier Airport, it is one of six airports that straddle the Canada–US border. The others are Whetstone International Airport, Coutts/Ross International Airport, International Peace Garden Airport, Piney Pinecreek Border Airport, and Coronach/Scobey Border Station Airport.

Why are there 6 airports that straddle the Canada–US border? That sounds too many to be just a coincidence.

Those strips of concrete keep Canada from floating away, they just conveniently double as airports.

These are, likely, the only true "international" airports in the world. All the rest are actually "intranational" since they only exist in one nation.

@FreeMan but then again, there is Basel Mulhouse Freiburg EuroAirport in France / Switzerland ;-) It officially serves cities of three countries, although it resides "only" in two.

I did say "likely". I figured there was at least one somewhere else...

Note that "things that span the US/Canada border" is a thing in itself.  For example, the "Haskell Free Library and Opera House" in Derby Line, VT and Stanstead, QC, is one of them.  There are American towns that are only accessible from Canada (Pt. Roberts, WA and Angle Inlet, MN).  When I grew up "the longest undefended border" was a point of pride, and folks tried to make a thing of it.

@FlorianAlbrecht there's also Geneva airport, part of which is built on former French territory and which has a French customs area so flights to and from France can operate as domestic flights without customs controls.  Still not the same as the US-Canada airports, but it would have been if not for the territory swap.

@RonBeyer Ssshh! Don't tell them!

@AJM There's nothing to hide!

There's no way to answer this as well as Half As Interesting did on youtube:

If you don't want to watch it, TLDR, the US had the Neutrality Act(s) and couldn't send war materiel. But it could effectively deliver them to the border.
It was loophole in early WW2 for the US to remain "neutral" but get materiel to Europe. Here's what the British Purchasing Commission wikipedia page says:

Aircraft purchased by the Commission first had to be moved across the border into Canada, due to the US' neutrality laws, it being illegal to transport 'war materials' direct from US ports.

Half as Interesting also says Piney Pinecreek wasn't one of those airports. It's the exception to the loophole.

Effectively, then, the aircraft landed in the US, but rolled to a stop in Canada. Once they're technically in Canada, there's nothing we can do to prevent those crazy Canadians from flying them elsewhere? That's a pretty clever work around!

Actually, the process of crossing the border was somewhat more complex http://56755.blogspot.com/2007/07/ww-ii-planes-cross-border-by-pembina.html

As I understood it, they didn't rolled to a stop in Canada, as that was forbidden by the Act. IMHO, the most important part of the video, is in fact that "Canadian citizens would hitch the empty planes to horses or tractors and drag them to the Canadian side"